This application claims the priority of German patent application 102 19 216.2, filed 29 Apr. 2002, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and apparatus for processing a navigation signal of a satellite navigation system. In addition to the well known GPS, there are other satellite navigation systems, such as GLONASS and the planned GALILEO system.
It is known that navigation signals can be modulated by a Binary Offset Coding (BOC) method, as discussed, for example in J. W. Betz: “Design and Performance of Code Tracking for the GPS M Code Signal”, the MITRE Corporation, September 2000.
One object of the present invention is to provide an improved method for processing a navigation signal received from a satellite navigation system, which navigation signal is generated by modulating navigation codes using a complex BOC signal. (As used herein, the term “complex signal” refers to the mathematical concept of complex numbers, and not to a possible complexity of the signal structure.)
This and other objects and advantages are achieved by the processing method and apparatus according to the invention. On the one hand, the invention comprises a method of processing a signal received from a satellite navigation system. Without limiting the invention, the special examples described hereinafter are, as a rule, based on four navigation codes, which may be intended for or accessible to different applications or user groups. The codes may, for example, be different civil and military navigation codes; or codes of varying precision may be provided which can be processed by different user groups or terminals depending on the access authorization.
According to the invention, the navigation codes are modulated by a complex BOC signal with a defined subcarrier frequency. Basically, a suitable BOC modulation of the navigation codes can be selected such that the resulting signal has a constant amplitude. The latter signal is then modulated by a carrier signal to generate a navigation signal having an envelope of a constant amplitude. The carrier signal is, for example, on the order of 1 GHz or more (e.g., 1.0-2.0 GHz). The navigation codes may have a frequency of several MHz or several tens of MHz (e.g., between 5 MHz and 20 MHz). The subcarrier frequency may be on the order of several MHz or several tens of MHz (e.g., between 10 and 50 MHz).
According to the invention, processing of the navigation signal comprises a complex correlation of the received navigation signal with at least one reference signal. Each reference signal is formed by multiplication of one of the navigation codes by a subcarrier signal that corresponds to a signal for a matched filtering of those fractions of the navigation signal which contain the respective navigation code. Thus, reference signals are generated which, in a correlation, interact with those fractions of the navigation signal that (expressed as a mathematical notation) contain the corresponding navigation code by which the subcarrier signal is multiplied.
According to a further feature of the invention, the navigation signal is correlated with at least one reference signal which occurs as a summand formed by transformation of the navigation signal to a sum of subcarrier signals, taking into account of the characteristics of the navigation codes. It is therefore observed within the framework of the transformation how the navigation codes behave, particularly when they may assume which values. A corresponding transformation of the navigation signal to a sum of individual subcarrier signals as components of the navigation signal can then be carried out. This transformation can take place before implementation of the method according to the invention, and the result of the transformation can be correspondingly implemented within the scope of the process.
In particular (for example, for the special case of four navigation codes), processing of the navigation signal takes place by a complex correlation with at least one reference signal with:
            r      1        =                  e        1            ·      C      ·              [                              ·                          sign              ⁡                              (                                  cos                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                                                                          ⁢                                              f                        s                                            ⁢                      t                                        )                                                  )                                              +                      jsign            ⁡                          (                              sin                ⁡                                  (                                      2                    ⁢                    π                    ⁢                                                                                  ⁢                                          f                      s                                        ⁢                    t                                    )                                            )                                +                                    (                              1                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            +                                              π                        /                        4                                                              )                                                  )                                              +                                    (                                                -                  1                                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            -                                              π                        /                        4                                                              )                                                  )                                                    ⁢                                  ]                        r      2        =                                        e            2                    ·          C          ·                      [                                          ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                                            -                      1                                        -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                          ⁢                                  ⁢                  r          3                    =                                                  e              3                        ·            C            ·                          [                                                ·                  j                  ·                                      sign                    ⁡                                          (                                              cos                        ⁡                                                  (                                                      2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    )                                                                    )                                                                      +                                  jsign                  ⁡                                      (                                          sin                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                  +                                                      (                                                                  -                        1                                            +                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        +                                                          π                              /                              4                                                                                )                                                                    )                                                                      +                                                      (                                                                  -                        1                                            -                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        -                                                          π                              /                              4                                                                                )                                                                    )                                                                                  ]                                ⁢                                          ⁢                      r            4                          =                              e            4                    ·          C          ·                      [                                          ·                j                ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    +                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                              wherein, e1, e2, e3, e4 represent the navigation codes, and fs corresponds to the subcarrier frequency of the BOC signal. C is a constant.
In particular, it is provided that, as a result of the complex correlation of the navigation signal with at least one reference signal, a time offset between a navigation code and a reference signal is determined. As a result, the method according to the invention can be used to synchronize a navigation code and the corresponding reference signal, which represents a basis for a position determination.
For a transmission of the navigation signal to a terminal, as a rule, an additional modulation is provided. Thus, as described above, the navigation signal is further modulated by a carrier signal. Before the complex correlation, the carrier signal is first preferably demodulated.
In addition, the present invention provides a terminal for a satellite navigation system which has at least one receiving device and a complex correlation unit for receiving and processing a navigation signal. According to the invention, the complex correlation unit has at least one complex correlator that generates at least one reference signal. Each reference signal is formed by multiplication of the navigation code by a subcarrier signal that corresponds to a signal for a matched filtering of those fractions of the navigation signal that contain the respective navigation code. Particularly the above statements concerning the method according to the invention can apply analogously to the other characteristics, details and advantages of the terminal according to the invention.
In a preferred embodiment of the invention, the complex correlator generates at least one reference signal as a summand of a transformation of the navigation signal to a sum of subcarrier signals taking into account the characteristics of the navigation codes. In particular, it may be provided that the complex correlation unit has at least one complex correlator which generates at least one reference signal with:
            r      1        =                  e        1            ·      C      ·              [                              ·                          sign              ⁡                              (                                  cos                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                                                                          ⁢                                              f                        s                                            ⁢                      t                                        )                                                  )                                              +                      jsign            ⁡                          (                              sin                ⁡                                  (                                      2                    ⁢                    π                    ⁢                                                                                  ⁢                                          f                      s                                        ⁢                    t                                    )                                            )                                +                                    (                              1                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            +                                              π                        /                        4                                                              )                                                  )                                              +                                    (                                                -                  1                                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            -                                              π                        /                        4                                                              )                                                  )                                                    ⁢                                  ]                        r      2        =                                        e            2                    ·          C          ·                      [                                          ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                                            -                      1                                        -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                          ⁢                                  ⁢                  r          3                    =                                                  e              3                        ·            C            ·                          [                                                ·                  j                  ·                                      sign                    ⁡                                          (                                              cos                        ⁡                                                  (                                                      2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    )                                                                    )                                                                      +                                  jsign                  ⁡                                      (                                          sin                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                  +                                                      (                                                                  -                        1                                            +                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        +                                                          π                              /                              4                                                                                )                                                                    )                                                                      +                                                      (                                                                  -                        1                                            -                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        -                                                          π                              /                              4                                                                                )                                                                    )                                                                                  ]                                ⁢                                          ⁢                      r            4                          =                              e            4                    ·          C          ·                      [                                          ·                j                ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    +                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                              
“Complex correlation unit” and “complex correlator” should be understood here also in the mathematical sense of complex numbers; thus, they are devices that are constructed for the processing of signals having a real part and an imaginary part. By means of such a terminal, navigation signals that contain at least four navigation codes and were modulated with a suitable complex BOC signal with a constant envelope can be processed.
In particular, it is provided that the complex correlation unit is constructed such that, by means of the at least one complex correlator, a time offset is determined between a navigation code of the navigation signal and a reference signal.
For transmission of the navigation signal to a terminal, as a rule, an additional modulation is provided. Thus, as a rule, the navigation signal is additionally modulated by means of a carrier signal. It is therefore preferably provided that a demodulation device for the demodulation of a carrier signal is connected in front of the complex correlation unit.
The terminal may be constructed as a user terminal (for example, as a portable terminal or as a terminal which is integrated in a landcraft, watercraft or aircraft). It may be constructed either for receiving navigation signals of a single satellite navigation system or of navigation signals of several satellite navigation systems, such as a combined GPS-GALILEO terminal. The user terminal may, for example, also be constructed as a combined terminal of a radio communications system and of a satellite navigation system, for example, as a mobile telephone which also has devices for the satellite navigation, or as a satellite navigation terminal which also has devices for data exchange via a mobile radio communications system.
Another object of the invention is to provide a computer program for controlling a complex correlation unit of a terminal for a satellite navigation system. In this case, the computer program is constructed for controlling at least one complex correlator for generating at least one reference signal. Each reference signal is formed by multiplication of one of the navigation codes by a subcarrier signal that corresponds to a signal for matched filtering of those fractions of a navigation signal which contain the respective navigation code. Particularly the above statements concerning the method according to the invention can analogously apply to the other characteristics, details and advantages of the computer program according to the invention.
In a further preferred embodiment of the invention, the at least one correlator for generating at least one reference signal is controlled to form a reference signal as the summand of a transformation of the navigation signal to a sum of subcarrier signals while taking into account the characteristics of the navigation codes.
In still another embodiment of the invention, the computer program according to the invention is constructed to control at least one complex correlator for generating at least one reference signal:
            r      1        =                  e        1            ·      C      ·              [                              ·                          sign              ⁡                              (                                  cos                  ⁡                                      (                                          2                      ⁢                      π                      ⁢                                                                                          ⁢                                              f                        s                                            ⁢                      t                                        )                                                  )                                              +                      jsign            ⁡                          (                              sin                ⁡                                  (                                      2                    ⁢                    π                    ⁢                                                                                  ⁢                                          f                      s                                        ⁢                    t                                    )                                            )                                +                                    (                              1                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            +                                              π                        /                        4                                                              )                                                  )                                              +                                    (                                                -                  1                                +                j                            )                        ·                                          2                            2                        ·                          sign              ⁡                              (                                  sin                  ⁡                                      (                                                                  2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            -                                              π                        /                        4                                                              )                                                  )                                                    ⁢                                  ]                        r      2        =                                        e            2                    ·          C          ·                      [                                          ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                                            -                      1                                        -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                          ⁢                                  ⁢                  r          3                    =                                                  e              3                        ·            C            ·                          [                                                ·                  j                  ·                                      sign                    ⁡                                          (                                              cos                        ⁡                                                  (                                                      2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    )                                                                    )                                                                      +                                  jsign                  ⁡                                      (                                          sin                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                  +                                                      (                                                                  -                        1                                            +                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        +                                                          π                              /                              4                                                                                )                                                                    )                                                                      +                                                      (                                                                  -                        1                                            -                      j                                        )                                    ·                                                            2                                        2                                    ·                                      sign                    ⁡                                          (                                              sin                        ⁡                                                  (                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              f                                s                                                            ⁢                              t                                                        -                                                          π                              /                              4                                                                                )                                                                    )                                                                                  ]                                ⁢                                          ⁢                      r            4                          =                              e            4                    ·          C          ·                      [                                          ·                j                ·                                  sign                  ⁡                                      (                                          cos                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                    ⁢                          t                                                )                                                              )                                                              -                              jsign                ⁡                                  (                                      sin                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                        t                                            )                                                        )                                            +                                                (                                      1                    +                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    +                                                      π                            /                            4                                                                          )                                                              )                                                              +                                                (                                      1                    -                    j                                    )                                ·                                                      2                                    2                                ·                                  sign                  ⁡                                      (                                          sin                      ⁡                                              (                                                                              2                            ⁢                            π                            ⁢                                                                                                                  ⁢                                                          f                              s                                                        ⁢                            t                                                    -                                                      π                            /                            4                                                                          )                                                              )                                                                        ]                              
Finally, the present invention comprises a computer program that is constructed to interact with a terminal of a satellite navigation system, and contains a machine-readable program carrier on which an above-described computer program is stored in the form of electronically readable control signals. The control signals can be stored in any suitable form read electronically by electrical, magnetic, electro-magnetic, electro-optical or other electronic methods. Examples of such program carriers are magnetic tapes, floppy disks, hard disks, DC-ROMs or semiconductor devices.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.